1. Technical Field
The present invention is related generally to digital computers, and more specifically to a system and method for executing application programs over a distributed network.
2. Background Art
As small computers continue to become more powerful, and their costs decrease, networks of computers continue to become more common. These networks can be connected using a variety of network architectures, and typically consist of a moderate to large number of nodes. Each node can be a stand alone computer system, or a network shared resource such as a file server or printer.
In some networks, it is common for a user at one node to wish to execute a program or access data which resides on another node. Such execution or access can be accomplished in several different ways. The user can copy the necessary files from the remote node to his own local node, and process them locally. It is also possible to have the local node, typically a workstation or desktop computer, emulate a simple terminal, and access the remote node. Under the second arrangement, commands are entered from, and results displayed on, the local node, while all processing takes place on the remote node.
A third technique is to execute an applications program on the local node which communicates to the remote node in a manner transparent to the user. The local applications program can send commands to the remote node in order to access data or cause execution of programs on the remote node.
The techniques just described have several obvious limitations and drawbacks. The technique of copying data and programs to a local node, not in general use on sophisticated networks, spends large amounts of time copying files which may be quite large in comparison to the amount of data actually needed. Also, creating multiple copies of files introduces a serious data coherency problem, in that it is difficult to reflect updates to a central location in a timely manner.
Using a local node to emulate a simple terminal minimizes the copying of large files from one node to another, but still uses a fairly large share of network communication resources. Everything typed at the local terminal, and everything displayed thereon, requires transmission of information over the network. Using an applications program running on the local node to interface with a user and send encoded commands to the remote node can decrease the amount of information transmitted, but does not entirely eliminate the problem.
For example, it is common for a central database to be connected to a network for access by the other nodes. The database can be accessed with special commands, such as those used in a Structured Query Language (SQL). Each SQL statement defines a single request to the database. As used herein, a transaction is an integral piece of work which, when completed, is committed to the database. All changes to the database are tentative until committed, so that an interrupted transaction can be rolled back, leaving the database in the same state it was before the transaction began. A series of database requests are generally needed to perform a single transaction.
When an application is running on a local node, and communicating with a database manager on a remote, or server, node, each request in a transaction requires two communications over the network. The database request must first be transmitted from the local node to the database server, and the results must be returned to the local node. Thus, if a single transaction requires 7 database requests, 14 separate messages must be communicated over the communications network.
It would be desirable for a system which runs application programs on remote nodes to minimize the network communications resources required for such processing.